The chlorinated dibenzo-p-dioxins (CDBD's) are a class of widespread environmental pollutants of considerable current concern. They occur as contaminants in commercial chlorophenols and especially as side products of the manufacture of chlorophenoxyacids. The main chlorodibenzo-p-dioxin found as a contaminant of the popular herbicide 2,4,5-trichlorophenoxyacetic acid (hereinafter referred to as "2,4,5-T") is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), possibly the most toxic man-made chemical known. This compound has an acute oral LD.sub.50 of less than 1 microgram per kg in the guinea pig. Exposure of humans to this toxin has occurred inadvertently through the use of 2,4,5-T-contaminated waste oil and through industrial accidents such as the explosion of a manufacturing plant utilizing trichlorophenol in Sevesco, Italy in 1975. The defoliant mixture "Agent Orange", disseminated in vast quantities in Vietnam during the 1960's also contained a significant amount of TCDD.
TCDD is not the only highly toxic chlorinated dibenzo-p-dioxin. The 1,2,3,7,8-pentachloro-, 1,2,3,6,7,8-hexachloro- and 1,2,3,7,8,9-hexachloro isomers have toxicities comparable to that of TCDD, and only a few of the possible isomers have thus far undergone toxicity testing.
Until recently, the only analytical technique with sufficient sensitivity and specificity for determination of TCDD has been high resolution mass spectrometry [as described by R. Baughman et al in an article entitled "An Analytical Method for Detecting TCDD (dioxin) Levels of TCDD in Samples from Vietnam". Environ. Health Persp., 5,27-36,(1973)]. Gas chromatography combined with low or medium resolution mass spectrometry in either electron impact or chemical ionization modes [as described by J. R. Hass et al in an article entitled "Determination of Polychlorinated Dibenzo-p-Dioxins in Biological Samples by Negative Chemical Ionization Mass Spectrometry." Anal. Chem. 50/11, 1474-1479 (1978)] has been used recently to estimate levels of chlorodibenzo-p-dioxins (CDBD's) in addition to TCDD itself. The detection limits of these techniques are on the order of a few tens of picograms when the samples are free of interfering contaminants.
Because of the cost and complexity of gas chromatography-mass spectrometry instrumentation and the high degree of skill and experience needed in assays of this type, only a few laboratories are able to perform CDBD assays at the present time. This situation has resulted in a slow output of analytical data. Additionally, the lack of a confirmatory technique not based on mass spectrometry has tended to limit the confidence of those not trained in that specialty in the data presently available. For these reasons, the present inventors have developed an assay based on the highly sensitive and relatively specific technique of radioimmunoassay. They believe that this assay will be applicable both to screening samples to minimize the demand for mass spectrometric analysis by eliminating "negatives", and for routine monitoring of exposure in environments where specific CDBD's are known to be present.